There has been examined supplying electric power temporarily from electric vehicles incorporating secondary batteries, when electricity infrastructures become unavailable due to disaster or the like. In more details, an electric vehicle such as an electric drive vehicle (EV) and a plug-in hybrid drive vehicle (PHEV) is connected to an electric power wiring system (hereinafter referred to as “indoor wiring system”) installed in a facility such as a residence, a factory, and an office, and then electric power is supplied from the secondary battery in the electric vehicle to the indoor wiring system. This indoor wiring system normally receives commercial electric power from the commercial electric power system.
For example, in supplying electric power from the secondary battery in the electric vehicle to the indoor wiring system such as HEMS (Home Energy Management System), electric power discharged from the secondary battery to the indoor wiring system is controlled by use of a charging stand provided between a charge and discharge device incorporated in the electric vehicle and the indoor wiring system. This charging stand includes an electric leakage detector on an electric path from the electric vehicle to the indoor wiring system. When electric leakage is detected, the charging stand breaks the electric path from the electric vehicle to the indoor wiring system (e.g., see document 1 [JP 2012-170258 A]).
Rules for interconnecting electric vehicles incorporating secondary batteries (external power supplies) and the commercial power supply system have not been determined yet. In consideration of protection of the electric power system, it is required that output current from the external power supply do not give direct effects on the commercial power supply system. Also in consideration of protection of the charge and discharge device incorporated in the electric vehicle, it is preferable that current outputted from the commercial power supply system do not give direct effects on the charge and discharge device in the electric vehicle.